Adjustable dual-band link

ABSTRACT

A communication system utilizing an adjustable link has at least a first data transmission circuit including at least a first communication link circuit. The first communication link circuit has a baseband circuit and at least a passband circuit. The baseband circuit corresponds to a baseband sub-channel and the passband circuit corresponds to a passband sub-channel. The first communication link circuit also includes a circuit that distributes a first subset of a data stream having a first symbol rate to the baseband circuit and a second subset of the data stream having a second symbol rate to the passband circuit. The baseband sub-channel and the passband sub-channel are separated by an adjacent guardband of frequencies. The passband carrier frequency is adjusted to define the guardband and the guardband corresponds to a first notch in a channel response of a first communications channel.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.12/268,986, filed Nov. 11, 2008, now U.S. Pat. No. 7,599,422, issuedOct. 6, 2009, which is a continuation of U.S. patent application Ser.No. 12/030,700, filed Feb. 13, 2008, now U.S. Pat. No. 7,450,629, issuedNov. 11, 2008, which is a divisional of U.S. patent application Ser. No.11/022,469, filed Dec. 22, 2004, now U.S. Pat. No. 7,349,484, issuedMar. 25, 2008, which applications are incorporated by reference hereinin their entirety.

FIELD OF THE INVENTION

The present invention relates generally to the communication of data.More specifically, the present invention relates to the communication ofdata over frequency-selective channels having one or more notches.

BACKGROUND

In typical baseband transmission systems that employ equalizationtechniques for equalizing channels with low-pass characteristics, ausable bandwidth extends from near DC up to a maximum frequency that isdetermined by a high-frequency roll-off of a communications channel andsignal-to-noise (SNR) requirements of a receiver. Referring to FIG. 4,when a magnitude 310 of a channel response 324 is essentially amonotonically decreasing function of frequency 312, this limitation isstraight forward and baseband signaling is able to utilize the full,usable bandwidth of the channel. For example, if a system has adequateSNR with up to 50 dB of channel attenuation then the channel whosemagnitude 310 decreases monotonically at 41.6 dB/decade starting at 1GHz could support baseband signaling over a 0-12 GHz band offrequencies.

It is not unusual, however, for a channel response 314 to include one ormore significant notches, such as first notch 316, that result in alocal minimum in the magnitude 310. Notches may be associated withreflections (due to differences in impedance, parasitic capacitance andmanufacturing tolerances) and other non-idealities. At higherfrequencies, the channel response 314 recovers substantially beforefinally dropping again due to the ultimately low-pass nature of thechannel. For such channels, the use of baseband signaling, with a usablesignaling bandwidth limited from near DC up to the first notch 316, doesnot take advantage of all of the usable transmission bandwidth.Additional unutilized bandwidth is available at higher frequencies wherethe channel response 314 recovers from the first notch 316.Reconsidering the previously described example with the channel response314 having the first notch 316 in a notch band of frequencies 322between 4 and 4.5 GHz, the system could only support baseband signalingover a first band of frequencies 318 between 0-4 GHz. A second band offrequencies 320 between 4.5 and 12 GHz, which has less than 50 dB ofattenuation, cannot be used with baseband signaling due to the firstnotch 316. As a consequence, this usable transmission bandwidth is notused in the system. There is a need, therefore, for a signaling systemthat more effectively utilizes the available bandwidth for channelshaving low-pass characteristics with one or more significant notches.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, reference should be made tothe following detailed description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a block diagram illustrating a system with an adjustable link.

FIG. 2 a is a block diagram illustrating a transmission communicationlink circuit.

FIG. 2 b is a block diagram illustrating a transmission communicationlink circuit.

FIG. 3 a is a block diagram illustrating a receiving communication linkcircuit.

FIG. 3 b is a block diagram illustrating a receiving communication linkcircuit.

FIG. 4 is a schematic diagram illustrating two channel responses.

FIG. 5 is a flow diagram illustrating a method of operating anadjustable link.

FIG. 6 is a flow diagram illustrating a method of operating anadjustable link.

FIG. 7 is a block diagram illustrating a circuit having the function ofan oscilloscope, herein called an escope, in a receiving communicationlink circuit.

Like reference numerals refer to corresponding parts throughout thedrawings.

DETAILED DESCRIPTION OF EMBODIMENTS

In one embodiment of an adjustable link, a first transmissioncommunication link circuit has a transmission baseband circuit and atransmission passband circuit. The transmission baseband circuitcorresponds to a baseband sub-channel and the transmission passbandcircuit corresponds to a passband sub-channel. The first transmissioncommunication link circuit also includes a circuit that distributes afirst subset of a data stream having a first symbol rate to thetransmission baseband circuit and a second subset of the data streamhaving a second symbol rate to the transmission passband circuit. Thefirst symbol rate and the second symbol rate are each less than a symbolrate of the data stream. The baseband sub-channel and the passbandsub-channel are separated by an adjacent guardband of frequencies. Thepassband carrier frequency is adjusted to define the guardband and theguardband corresponds to a first notch in a channel response of a firstcommunications channel.

In some embodiments, the first communications channel is used forcommunication between first and second integrated circuits. In someembodiments, the first communication channel is a data bus.

In another embodiment, the link includes a first data receivingcommunication link circuit. The first receiving communication linkcircuit has a receiving baseband circuit and at least a receivingpassband circuit. The receiving baseband circuit corresponds to abaseband sub-channel and the receiving passband circuit corresponds to apassband sub-channel. The first receiving communication link circuitincludes a circuit that combines the first subset of a data streamhaving the first symbol rate from the baseband receiving circuit and thesecond subset of the data stream having the second symbol rate from thepassband receiving circuit into the data stream. The first symbol rateand the second symbol rate are each less than the symbol rate of thedata stream. The baseband sub-channel and the passband sub-channel areseparated by an adjacent guardband of frequencies. The passband carrierfrequency is adjusted to define the guardband and the guardbandcorresponds to the first notch in the channel response of the firstcommunications channel.

Reference will now be made in detail to embodiments, examples of whichare illustrated in the accompanying drawings. In the following detaileddescription, numerous specific details are set forth in order to providea thorough understanding of the present invention. However, it will beapparent to one of ordinary skill in the art that the present inventionmay be practiced without these specific details. In other instances,well-known methods, procedures, components, and circuits have not beendescribed in detail so as not to unnecessarily obscure aspects of theembodiments.

FIG. 1 illustrates an embodiment of a system 50 having a plurality ofadjustable links. A first integrated circuit 60 is coupled to a secondintegrated circuit 62 via a first communication channel. In the system50, the first communication channel is illustrated as a data bus havinga plurality of signal lines 66. In some embodiments, a length of thesignal lines 66 is less than 1 meter. In some embodiments, each signalline, such as signal line 66 a, has a respective channel response, whichmay be different from channel responses of the other signal lines 66.The first integrated circuit 60 has a plurality of data transmissionand/or receiving communication link circuits 64, henceforth denoted bytransmission/receiving communication link circuits 64, for transmittingand receiving data to and from the second integrated circuit 62. Thesecond integrated circuit 62 also has a plurality of data transmissionand/or receiving communication link circuits 68, henceforth denoted bytransmission/receiving communication link circuits 68, for transmittingand receiving data to and from the first integrated circuit 60.

Each data transmission/receiving communication link circuit, such asdata transmission/receiving communication link circuit 64 a, has arespective baseband circuit, such as baseband circuit 116 a in FIG. 2 aor 212 a in FIG. 3 a, and at least a respective passband circuit, suchas passband circuit 116 b in FIG. 2 a or 212 b in FIG. 3 a. Therespective baseband circuit corresponds to a baseband sub-channel in thefirst communications channel. In some embodiments, such as those wherethe first communications channel is ac-coupled, the respective basebandsub-channel does not contain DC. The passband circuit of a respectivedata transmission/receiving communication link circuit 64 corresponds toa passband sub-channel in the first communications channel. For arespective data transmission/receiving communication link circuit, arespective band of frequencies corresponding to the basebandsub-channel, such as band of frequencies 318 in FIG. 4, and a respectiveband of frequencies corresponding to the passband sub-channel, such asband of frequencies 320 in FIG. 4, are separated by a respectiveadjacent guardband of frequencies. The respective guardband offrequencies, such as the notch band of frequencies 322 in FIG. 4,correspond to a respective notch, such as the first notch 316 in FIG. 4,in a respective channel response of the first communications channel.

In some embodiments, the channel response is a transfer function of thefirst communication channel. In some embodiments, the channel responseis a step response of the first communication channel. In someembodiments, the channel response is an impulse or pulse response of thefirst communication channel.

The respective baseband sub-channel circuit and the respective passbandsub-channel circuit in the respective data transmission/receivingcommunication link circuit, such as data transmission/receivingcommunication link circuit 64 a, may be adjusted based on one or moreperformance characteristics of the first communication channelcorresponding to one or more respective signal lines, such as signalline 66 a. In particular, the respective band of frequenciescorresponding to the baseband sub-channel and/or the respective band offrequencies corresponding to the passband sub-channel may be adjusted soas to define the respective guardband of frequencies around a respectivenotch in the respective channel response. Control logic 78 in the firstintegrated circuit 60 determines the sub-channel settings for therespective data transmission/receiving communication link circuit. Thesub-channel settings for the respective baseband circuit may include oneor more low-pass filter corner frequencies and/or a respective clockrate. The sub-channel settings for the respective passband circuit mayinclude one or more respective bandpass filter bandwidths, a respectivecarrier frequency, a respective fundamental frequency and/or arespective clock rate. The sub-channel settings may be stored in amemory 76 a in the first integrated circuit 60. In some embodiments, thememory 76 a is separate from the control logic 78, while in otherembodiments the memory 76 a is embedded within the control logic 78.

The system 50 may include at least a second communications channel forcommunicating information, including communications channel circuit 70,communications channel circuit 74 and signal line 72. In someembodiments, the information may include sub-channel settings for one ormore data transmission/receiving communication link circuits 68 in thesecond integrated circuit 62. In other embodiments, the information mayinclude data used to train at least one of the datatransmission/receiving communication link circuits 64 or 68, such asdata transmission/receiving circuit 64 a or 68 a, during a training modeof operation.

In some embodiments, the sub-channel settings are stored in a memory 76b in the second integrated circuit 62. In the system 50, the secondcommunication channel includes a signal line 72. In some embodiments,the second communication channel may include two or more signal lines.In some embodiments, each pairing of data transmission/receivingcommunication link circuits in the first integrated circuit 60 and thesecond integrated circuit 62 may have a separate additional signal linein the second communications channel for communicating respectivesub-channel circuit settings.

In other embodiments, sub-channel circuit settings and/or data used totrain at least one of the data transmission/receiving communication linkcircuits 64 or 68 may be communicated using one or more of the signallines 66 in the first communication channel. For example, thesub-channel circuit settings may be transmitted from the firstintegrated circuit 60 at a slow data rate that is easily received by thesecond integrated circuit 62. Alternatively, the sub-channel circuitsettings may be transmitted from the first integrated circuit 60 to thesecond integrated circuit 62 using a dedicated small-bandwidth passbandsub-channel.

In some embodiments, the first communication channel may include one ormore additional notches in the channel response. In some embodiments,the data transmission/receiving communication link circuits 64 in thefirst integrated circuit 60 and the data transmission/receivingcommunication link circuits 68 in the second integrated circuit 62 mayinclude one or more additional passband circuits corresponding toadditional passband sub-channels. The band of frequencies correspondingto each additional passband sub-channel is separated from the band offrequencies of a lower passband sub-channel by a respective guardband offrequencies. A respective guardband of frequencies corresponds to arespective notch in the respective channel response of the firstcommunications channel.

The system 50 in FIG. 1 shows 3 data transmission/receivingcommunication link circuits 64 and 3 data transmission/receivingcommunication link circuits 68. In other embodiments, the system 50 mayhave 1, 2 or more than 3 pairs of data transmission/-receivingcommunication link circuits 64 and 68.

The system 50 in FIG. 1 illustrates a set of adjustable links forinter-chip communication. In some embodiments, the adjustable link maybe used for intra-chip communication, such as between modules in anintegrated circuit, such as the first integrated circuit 60.

In some embodiments, the combined bandwidth of the respective basebandsub-channel and the one or more passband sub-channels in the firstcommunication channel for each pair of data transmission/receivingcommunication link circuits 64 and 68 is more than 1 GHz, 2 GHz, 10 GHzor 12 GHz. In some embodiments, the band of frequencies corresponding tothe guardband is at least 0.25 GHz wide, 0.5 GHz wide, 1.0 GHz wide or2.0 GHz.

FIG. 2 a illustrates an embodiment of data transmission communicationlink circuit 100. The data transmission link circuit 100 uses multi-tonecommunication. A data stream 110 having a symbol rate is distributed bydemultiplexer 112 into a first subset 118 a of the data stream 110 and asecond subset 118 b of the data stream 110 based on clock signals 114.The first subset 118 a of the data stream 110 and the second subset 118b of the data stream 110 each have a symbol rate that is less than thesymbol rate of data stream 110. The first subset 118 a of the datastream 110 is coupled to the baseband circuit 116 a. The second subset118 b of the data stream 110 is coupled to the passband circuit 116 b.In some embodiments, the data transmission link circuit 100 may includeone or more additional passband circuits.

The baseband circuit 116 a and the passband circuit 116 b each include adigital-to-analog converter 120 and a transmit buffer 122. In someembodiments, the digital-to-analog converter 120 may also include aserializer. The transmit buffers 122 are coupled to adjustable clocksignals 138 that gate an output from the transmit buffers 122. The clocksignals 114 and the clock signals 138 may be generated from a commonsignal generator, such as a phase lock loop or a delay lock loop (forexample, using a voltage divider), or from separate signal generators.

The output from the transmit buffer 122 b is mixed in mixer 126 b withcarrier signal 130 b generated by oscillator 128, thereby shiftingsignals to the band of frequencies corresponding to the passbandsub-channel. In some embodiments, the mixer 126 b is a multiplier. Insome embodiments, more than one mixer may be used in a passband circuit,such as passband circuit 116 b. In some embodiments, the carrier signal130 b may be a sinusoidal or harmonic signal having an adjustablecarrier frequency. In other embodiments, the carrier signal 130 b may bea square-wave signal having an adjustable fundamental frequency. Outputsfrom the baseband circuit 116 a and the passband circuit 116 b arecombined in adder 134 prior to the transmission of signal 136 in thefirst communication channel.

In some embodiments, the baseband circuit 116 a and the passband circuit116 b may modulate the first subset 118 a of the data stream 110 and/orthe second subset 118 b of the data stream 110, respectively. In someembodiments, the modulation in the baseband circuit 116 a is differentfrom that used in the passband circuit 116 b, which is also referred toas bit-loading. Suitable modulation in the baseband circuit 116 aincludes 2 or more level pulse amplitude modulation (PAM), such astwo-level PAM or four-level PAM. Suitable modulation in the passbandcircuit 116 b includes 2 or more level pulse amplitude modulation (PAM),also referred to as on-off keying, and, as discussed below, 2 or morelevel quadrature amplitude modulation (QAM) for passbands that are inquadrature with one another. Other suitable modulations include pulseposition modulation (PPM) and pulse width modulation (PWM). In someembodiments, the modulation in one or more respective sub-channels ofone of the data transmission/receiving link circuits, such as datatransmission/receiving link circuit 64 a in FIG. 1, may be differentfrom that used in the other data transmission/receiving link circuits(e.g., link circuits 64 b and 64 c, FIG. 1).

The data transmission link circuit 100 does not include filters to limitthe band of frequencies corresponding to the baseband sub-channel andthe passband sub-channel. Instead, use is made of the fact that arectangular function corresponding to a bit cell in the time domaincorresponds to a sinc function in the frequency domain, and that amagnitude of a first sideband of the sinc function is 20 dB less thanthe magnitude of its peak. In some embodiments, the respective band offrequencies corresponding to the respective guardband may therefore beadjusted by appropriately setting one or more of the clock signals 138(and thus the corresponding bit cell times) and/or the carrier orfundamental frequency of the carrier signal 130 b.

In the absence of band limiting associated with filters, however, thedata transmission link circuit 100, will have constraints on how hardthe transmit buffers 122 may be driven. In particular, in embodimentswith additional passband circuits, transmit power may be reduced inorder to ensure that there is sufficient voltage swing available for thetransmit buffers 122. This may result in poorer performance, forexample, a higher error rate.

FIG. 2 b illustrates an embodiment of data transmission communicationlink circuit 150. The baseband circuit 116 a and the passband circuit116 b contain an adjustable low-pass filter 124. In some embodiments,one or more low-pass filters 124 may have fixed characteristics thatcannot be dynamically adjusted during normal operation of the linkcircuit 150. The passband circuit 116 b also includes an adjustablebandpass filter 132 b. Therefore, in addition to setting one or moreclock signals 138 and/or the carrier or fundament frequency of thecarrier signal 130 b, the respective band of frequencies correspondingto the respective guardband may be adjusted by setting a cornerfrequency of the low-pass filter 124 a, a corner frequency of thelow-pass filter 124 b and/or a bandwidth of the bandpass filter 132 b.In addition to the added degrees of freedom in adjusting the respectiveguardband, the low-pass filters 124 and the bandpass filter 132 b alsoreduce the transmit power constraints associated with additionalsub-channels described previously.

FIG. 2 b also illustrates an optional third subset 118 c of thedatastream 110 and an optional passband circuit 116 c with acorresponding passband sub-channel that is in quadrature with thatassociated with passband circuit 116 b. The oscillator 128 generates acarrier signal 130 c that is 90° out of phase with the carrier signal130 b. The carrier signal 130 b and the carrier signal 130 c can also bedescribed as a vector having an in-phase component and an out-of-phasecomponent. Thus, the passband corresponding to the passband circuit 116b may be described as an in-phase passband and the passbandcorresponding to the passband circuit 116 c may be described as anout-of-phase passband. Other components (120 c, 122 c, 124 c, 126 c, 132c) in the passband circuit 116 c have functions corresponding to thosein the passband circuit 116 b. Note that the use of an additionalpassband sub-channel that is in quadrature also reduces the powerconstraint associated with additional sub-channels described previously.Also note that in some embodiments the data transmission link circuit150 may include one or more additional passband circuits and/oradditional pairs of passband circuits whose passband sub-channels are inquadrature.

FIGS. 2 a and 2 b illustrate embodiments of data transmission linkcircuits 100 and 200 that use so-called direct conversion. Otherembodiments may use so-called heterodyne conversion, where signals areconverted to one or more intermediate frequencies before conversion tobaseband. In these embodiments, more than one mixer, such as the mixer126 b, in a passband circuit, such as passband circuit 116 b, may beused. In addition, in some embodiments the low-pass 124 and the bandpassfilters 132 in FIG. 2 b, as well as in other embodiments below, may beexcluded.

FIG. 3 a illustrates an embodiment of data receiving communication linkcircuit 200. The data receiving link circuit 200 uses multi-tonecommunication. An input 210 received from the first communicationchannel is coupled to the baseband circuit 212 a and the passbandcircuit 212 b. In some embodiments, the data receiving link circuit 200may include one or more additional passband circuits.

The input is mixed in mixer 216 b with carrier signal 220 b generated byoscillator 218, thereby shifting signals from the band of frequenciescorresponding to the passband sub-channel. In some embodiments, themixer 216 b is a multiplier. In some embodiments, the passband circuit212 b includes more than one mixer, such as the mixer 216 b. In someembodiments, the carrier signal 220 b may be a sinusoidal or harmonicsignal having an adjustable carrier frequency. In other embodiments, thecarrier signal 220 b may be a square-wave signal having an adjustablefundamental frequency.

An output of the mixer 216 b in the passband circuit 212 b and the inputin the baseband circuit 212 a are coupled to receive buffers 224. Thereceive buffers 224 are coupled to adjustable clock signals 226 thatgate an output from the receive buffers 224. The baseband circuit 212 aand the passband circuit 212 b also include respective analog-to-digitalconverters 228 a, 228 b.

A first subset 230 a of a data stream is output by analog-to-digitalconverter 228 a, and a second subset 230 b of the data stream is outputby analog-to-digital converter 228 b. The first and second subsets 230a, 230 b of the data stream are coupled to multiplexer 232 and arecombined into a data stream 236 using clock signals 234.

The first and second subsets 230 a, 230 b of the data stream each have asymbol rate that is less than the symbol rate of data stream 236. Theclock signals 226 and 234 may be generated from a common signalgenerator, such as a phase lock loop or a delay lock loop (for example,using a divider), or from separate signal generators.

In some embodiments, the baseband circuit 212 a and the passband circuit212 b may demodulate the first subset 230 a of the data stream and/orthe second subset 230 b of the data stream, respectively. Thedemodulation reverses the modulation used in the corresponding datatransmission link circuit, such as data transmission link circuit 100(FIG. 2 a) on the other end of the communication channel. Theinformation necessary for accomplishing the demodulation may be providedto the data receiving link circuit 200 using the second communicationchannel. In some embodiments, the modulation in the baseband circuit 212a is different from that used in the passband circuit 212 b, which isalso referred to as bit-loading. Suitable demodulation in the basebandcircuit 212 a includes two or more level pulse amplitude modulation(PAM), such as two-level PAM or four-level PAM. Suitable demodulation inthe passband circuit 212 b includes two or more level pulse amplitudemodulation (PAM), also referred to as on-off keying, and two or morelevel quadrature amplitude modulation (QAM) for passbands that are inquadrature with one another. Other suitable modulation include pulseposition modulation (PPM) and pulse width modulation (PWM). In someembodiments, the demodulation in one or more sub-channels of one of thedata transmission/receiving link circuits, such as datatransmission/receiving link circuit 64 a in FIG. 1, may be differentfrom that used in other data transmission/receiving link circuits.

The data receiving link circuit 200 does not include filters to limitthe band of frequencies corresponding to the baseband sub-channel andthe passband sub-channel. Instead, use is made of the fact that arectangular function corresponding to the bit cell in the time domaincorresponds to the sinc function in the frequency domain and that themagnitude of the first sideband of the sinc function is 20 dB less thanthe magnitude of its peak. In some embodiments, the band of frequenciescorresponding to the guardband may therefore be adjusted byappropriately setting one or more of the clock signals 226 (and thus thecorresponding bit cell times) and/or the carrier or fundamentalfrequency of the carrier signal 220 b. Values of the clock signals 226and/or the carrier or fundamental frequency of the carrier signal 220 bcorrespond to those used in the corresponding data transmission linkcircuit, such as data transmission link circuit 100 (FIG. 1), on theother end of the communication channel. The information necessary forsetting these configuration values in the data receiving link circuit200 may be provided to the data receiving link circuit 200 using thesecond communication channel, a baseband sub-channel or a passbandsub-channel.

FIG. 3 b illustrates an embodiment of data receiving communication linkcircuit 250. The baseband circuit 212 a and the passband circuit 212 bcontain respective adjustable low-pass filters 222 a, 222 b. In someembodiments, one or more low-pass filters 222 may have fixedcharacteristics. The passband circuit 212 b also includes an adjustablebandpass filter 214 b. Therefore, in addition to setting one or moreclock signals 226 and/or the carrier or fundament frequency of thecarrier signal 220 b, the respective band of frequencies correspondingto the respective guardband may be adjusted by setting a cornerfrequency of a low-pass filter 222 a, a corner frequency of a low-passfilter 222 b and/or a bandwidth of the bandpass filter 214 b.

FIG. 3 b also illustrates an optional passband circuit 212 c with acorresponding passband sub-channel that is in quadrature with thatassociated with passband circuit 212 b. The oscillator 218 generates acarrier signal 220 c that is 90° out of phase with the carrier signal220 b. The carrier signal 220 b and the carrier signal 220 c can also bedescribed as a vector having an in-phase component and an out-of-phasecomponent. Thus, the passband corresponding to the passband circuit 212b may be described as an in-phase passband and the passbandcorresponding to the passband circuit 212 c may be described as anout-of-phase passband. The other components (214 c, 216 c, 222 c, 224 c,228 c) in the passband circuit 212 c have functions corresponding tothose in the passband circuit 212 b. The optional passband circuit 212 coutputs a third subset 230 c of the datastream. The values of thesettings for the corner frequencies of the low-pass filters 222 a, 222b, 222 c and the bandwidths of the bandpass filters 214 b, 214 ccorrespond to those used in the corresponding data transmission linkcircuit, such as data transmission link circuit 150 (FIG. 2 b), on theother end of the communication channel. These may be provided to thedata receiving link circuit 200 using the second communication channel.Also note that in some embodiments the data receiving link circuit 250may include one or more additional passband circuits and/or additionalpairs of passband circuits whose passband sub-channels are inquadrature.

FIGS. 3 a and 3 b illustrate embodiments of data receiving link circuits200 and 250 that use so-called direct conversion. Other embodiments mayuse so-called heterodyne conversion, where signals are converted to oneor more intermediate frequencies before conversion to baseband. In theseembodiments, more than one mixer, such as the mixer 216 b, in a passbandcircuit, such as passband circuit 212 b, may be used. In addition, insome embodiments the low-pass 214 and the bandpass filters 222 in FIG. 3b may be excluded.

The data transmission link circuit 150 and the data receiving linkcircuit 250 illustrate adjustable analog filters. In other embodiments,the adjustable filters may be implemented in a digital domain afteranalog-to-digital conversion, for example, as an FIR filter.

FIG. 5 is a flow diagram illustrating an embodiment of a method orprocess for transmission of data using an adjustable link. A pluralityof subsets of the data stream are received 512. These are converted intorespective analog signals 514. In some embodiments, the respectiveanalog signals are low-pass filtered using respective filters havingrespective adaptive corner frequencies 516. For sub-channels other thanbaseband, the respective analog signals are mixed with respectivevectors having respective adaptive carrier or fundamental frequencies toproduce respective sub-channel signals 518. In some embodiments, mixingis accomplished using signal multiplication. In some embodiments, therespective sub-channel signals are bandpass filtered using respectivefilters having respective adaptive bandwidths 520. The respectivesub-channel signals are combined prior to transmission 522 to produce acomposite signal for transmission across a communication channel. Tasks512 through 522 may be performed continuously, in pipeline fashion, on acontinuing data stream. By adjusting one or more bands of frequencies,such as the first band of frequencies 318 (FIG. 4) or the second band offrequencies 320 (FIG. 4), at least one adjacent guardband of frequenciescorresponding to one or more notches, such as notch band of frequencies322, may be defined.

FIG. 6 is a flow diagram illustrating an embodiment of a method orprocess for receiving data using the adjustable link. An input signal isreceived 612. In some embodiments, the signal is bandpass filtered usingrespective bandpass filters having respective adaptive bandwidths 614 toproduce a set of sub-channel signals. The sub-channel signals, otherthan the baseband sub-channel signal, are mixed with respective vectorshaving respective adaptive carrier or fundamental frequencies to downconvert the respective sub-channel signals 616. In some embodiments, themixing is accomplished using signal multiplication. In some embodiments,the resulting sub-channel signals are low-pass filtered using respectivefilters having respective adaptive corner frequencies 618. Thesub-channel signals are converted into digital values corresponding torespective subsets of the data stream 620. The sub-sets of the datastream are combined 622 to produce a recovered data stream. Tasks 612through 522 may be performed continuously, in pipeline fashion, on asuccessive portions of a received signal so as to produce a continuingdata stream. Once again, by adjusting one or more bands of frequencies,such as the first band of frequencies 318 (FIG. 4) or the second band offrequencies 320 (FIG. 4), at least one adjacent guardband of frequenciescorresponding to one or more notches, such as notch band of frequencies322, may be defined.

Referring to FIG. 1, for one or more respective datatransmission/receiving communication link circuits 64 (FIG. 1) and/orone or more data transmission/receiving communication link circuits 68(FIG. 2), characteristics of the communication channel, such as signalline 66 a, may be determined jointly or independently. In addition, forthe respective data transmission/receiving communication link, thecommunication channel may be characterized for one or more respectivesub-channels. In some embodiments, such channel characterization may usea circuit having the function of an oscilloscope, herein called anescope 700, as illustrated in FIG. 7. The escope 700 is coupled torespective sub-channel signals in one or more data receivingcommunication link circuits, such as data receiving communication linkcircuit 200 (FIG. 3 a) and data receiving communication link circuit 250(FIG. 3 b), between the receive buffer 224 (FIGS. 3 a and 3 b) and theanalog-to-digital converter 228 (FIGS. 3 a and 3 b). Analog signals 710corresponding to a respective sub-channel are coupled to comparators712. The escope 700 is intended for use with 2-PAM modulation. By addingadditional comparators 712 it may be extended to an arbitrarymulti-level modulation. Each comparator has a respective referencevoltage 714. In some embodiments, one reference voltage, such asreference voltage 714 a, corresponds to a logical 1 or high voltagestate and another, such as reference voltage 714 b, to a logical 0 or alow voltage state. In other embodiments, one reference voltage may befixed and another reference voltage may be varied. For example, onereference voltage may be at threshold, i.e., a data slicer, and one maybe anywhere in the eye pattern. In embodiments with multi-levelmodulation, multiple samples may be taken. Outputs from the comparators712 are coupled to an XOR gate or logical comparator 716, whichgenerates an output 718. The XOR gate or logical comparator 716 may beimplemented in hardware or software. By adjusting one or the referencevoltages 714 (for example, using the control logic 78 in FIG. 1), theoutput 718 corresponds to a cross-section of a portion of an eyepattern. The portion of the eye pattern corresponds to a logical 0 or 1decision at a respective sample time. In this way, a voltage margin maybe determined.

By further adjusting one or more of the respective clock signals 226(FIGS. 3 a and 3 b), cross-sections of the eye pattern at differentsample times may be determined using the escope 700. In this way, atiming margin may also be determined. Such voltage and timing marginmeasurements allow characteristics of the communication channel to bedetermined. In some embodiments, the channel may also be characterizedbased on a bit error rate and/or the pulse response in one or moresub-channels in a respective data transmission/receiving link circuit,such as data transmission/receiving link circuit 64 a (FIG. 1). In someembodiments, the channel may also be characterized based on a bit errorrate and/or the pulse response in one or more of datatransmission/receiving link circuits 64 or data transmission/receivinglink circuits 68.

In other embodiments, the escope 700 may be used to characterize achannel, including one or more notches, such as the first notch 316(FIG. 4), in the frequency domain. Such a frequency-domain measurementmay be performed using a dedicated measurement channel having a singlemixer and no low-pass or band-pass filters. Alternatively, the cornerfrequencies of one or more low-pass and/or bandpass filters in asub-channel circuit, such as passband sub-channel 116 c (FIG. 2 b), maybe appropriately adjusted and any additional mixers may be disabled.While other sub-channels are disabled, a DC-signal may be transmittedover the dedicated measurement channel or the respective sub-channel. Byvarying the carrier frequency of the sinusoidal or harmonic signalgenerated by an oscillator, such as oscillator 128 (FIG. 2 b), afrequency range of interest may be swept. At each carrier frequency, theescope 700 may be used to measure a maximum received signal magnitude,which is inversely proportional to the channel loss.

After determining one or more channel characteristics, a respectivelow-pass filter corner frequency, a respective clock signal, arespective bandpass filter bandwidth and/or a respective carrier orfundamental frequency may be adjusted by control logic 78 (FIG. 1) forone or more sub-channels in one or more data transmission/receivingcircuits, such as data transmission/receiving circuit 64 a (FIG. 1). Insome embodiments, determination of one or more channel characteristicsand adjustment of one or more sub-channel circuit values, such as thoselisted above, in one or more data transmission/receiving circuits, suchas data transmission/receiving circuit 64 a (FIG. 1), may be repeatediteratively.

In some embodiments, in the respective data transmission/receivingcircuit, such as data transmission/receiving circuit 64 a (FIG. 1), aband of frequencies corresponding to a respective sub-channel, such asthe first band of frequencies 318 (FIG. 4), may be fixed and anotherband of frequencies, such as the second band of frequencies 320 (FIG.4), may be an integer multiple of the first band of frequencies 318(FIG. 4). This allows the use of a single clock in determining one ormore eye patterns for one or more sub-channels using the escope 700.

Some embodiments of the data transmission/receiving circuits, such asdata transmission/receiving circuit 64 a (FIG. 1), may also includepreceding, transmission equalization and/or receiving equalization.

The adjustable link apparatus and method are well-suited for use incommunication between two or more semiconductor chips or dies, forexample, in electronic interconnects and data buses. In particular, theapparatus and method are well-suited for use in improving theutilization of available bandwidth in communication channels betweensemiconductor chips on the same printed circuit board (PCB) or betweensemiconductor chips on different printed circuit boards that areconnected through a backplane, signal lines or a coaxial cable at datarates exceeding multiple Gbps (gigabits per second), for example ratesof at least 2, 5 or 10 Gbps, depending on the embodiment.

The adjustable link apparatus and method are also well-suited for use inimproving communication between modules in an integrated circuit. Theadjustable link may be used in communication between a memory controllerchip and a dynamic random access memory (DRAM) chip. The DRAM chip maybe either on the same printed circuit board as the controller orembedded in a memory module. In addition, the adjustable link apparatusand method are also well-suited for use in improving communication atdata rates exceeding multiple Gbps, such as 2, 5 or 10 Gbps, dependingon the embodiment, between a buffer chip and a DRAM chip, both of whichare on the same memory module. The apparatus and methods describedherein may also be applied to other memory technologies, such as staticrandom access memory (SRAM) and electrically erasable programmableread-only memory (EEPROM).

Devices and circuits described herein can be implemented using computeraided design tools available in the art, and embodied by computerreadable files containing software descriptions of such circuits, atbehavioral, register transfer, logic component, transistor and layoutgeometry level descriptions stored on storage media or communicated bycarrier waves. Data formats in which such descriptions can beimplemented include, but are not limited to, formats supportingbehavioral languages like C, formats supporting register transfer levelRTL languages like Verilog and VHDL, and formats supporting geometrydescription languages like GDSII, GDSIII, GDSIV, CIF, MEBES and othersuitable formats and languages. Data transfers of such files on machinereadable media including carrier waves can be done electronically overthe diverse media on the Internet or through email, for example.Physical files can be implemented on machine readable media such as 4 mmmagnetic tape, 8 mm magnetic tape, 3½ inch floppy media, CDs, DVDs andso on.

The foregoing descriptions of specific embodiments of the presentembodiments are presented for purposes of illustration and description.They are not intended to be exhaustive or to limit the invention to theprecise forms disclosed. Rather, it should be appreciated that manymodifications and variations are possible in view of the aboveteachings. The embodiments were chosen and described in order to bestexplain the principles of the invention and its practical applications,to thereby enable others skilled in the art to best utilize theinvention and various embodiments with various modifications as aresuited to the particular use contemplated.

1. A data transmission circuit, comprising: a first communication linkcircuit, including: a baseband circuit and at least a passband circuit,the baseband circuit corresponding to a baseband sub-channel and thepassband circuit corresponding to a passband sub-channel; and a circuitto distribute a first subset of a data stream having a first symbol rateto the baseband circuit and a second subset of the data stream having asecond symbol rate to the passband circuit, the first symbol rate andthe second symbol rate each being less than a symbol rate of the datastream, wherein the baseband sub-channel and the passband sub-channelare separated by an adjacent guardband of frequencies corresponding to afirst notch in a channel response of a first communications channel. 2.The data transmission circuit of claim 1, wherein the basebandsub-channel and the passband sub-channel each have a bandwidth more than1 GHz.
 3. The data transmission circuit of claim 1, wherein theguardband has a width of at least 0.25 GHz.
 4. The data transmissioncircuit of claim 1, wherein the first communications channel has alength less than one meter.
 5. The data transmission circuit of claim 1,further comprising a first low-pass filter in the baseband circuit and asecond low-pass filter in the passband circuit, wherein at least one ofthe first low-pass filter and the second low-pass filter has arespective adjustable corner frequency, wherein the respectiveadjustable corner frequency and a carrier frequency of the passbandsub-channel together define the guardband between the basebandsub-channel and the passband sub-channel.
 6. The data transmissioncircuit of claim 1, further comprising a bandpass filter having anadjustable bandwidth in the passband circuit.
 7. The data transmissioncircuit of claim 1, further comprising a first converter in the basebandcircuit and a second converter in the passband circuit, the firstconverter to receive the first subset of the data stream and convert thefirst subset of the data stream into a first analog signal and thesecond converter to receive the second subset of the data stream andconvert the second subset of the data stream into a second analogsignal, wherein the first analog signal corresponds to the basebandsub-channel.
 8. The data transmission circuit of claim 7, furthercomprising a multiplier in the passband circuit, the multiplier tomultiply the second analog signal by a vector to produce a signalcorresponding to the passband sub-channel, wherein the vectorcorresponds to a carrier frequency of the passband sub-channel.
 9. Thedata transmission circuit of claim 8, wherein the vector has an in-phasecomponent and an out-of-phase component.
 10. The data transmissioncircuit of claim 1, further comprising a combiner to combine signals inthe baseband sub-channel and the passband sub-channel prior totransmission.
 11. A method of transmitting data, comprising: receiving adata stream having a symbol rate; distributing a first subset of thedata stream to a baseband circuit, the first subset of the data streamhaving a first symbol rate that is less than the symbol rate of the datastream, the baseband circuit corresponding to a baseband sub-channel;and distributing a second subset of the data stream to a passbandcircuit, the second subset of the data stream having a second symbolrate that is less than the symbol rate of the data stream, the passbandcircuit corresponding to a passband sub-channel; wherein the basebandsub-channel and the passband sub-channel are separated by an adjacentguardband of frequencies corresponding to a first notch in a channelresponse of a first communications channel.
 12. The method of claim 11,wherein the baseband sub-channel and the passband sub-channel each havea bandwidth more than 1 GHz.
 13. The method of claim 11, wherein theguardband has a width of at least 0.25 GHz.
 14. The method of claim 11,wherein the first communications channel has a length less than onemeter.
 15. The method of claim 11, further comprising: filtering thefirst subset of the data stream with a first low-pass filter in thebaseband circuit; and filtering the second subset of the data streamwith a second low-pass filter in the passband circuit, wherein at leastone of the first low-pass filter and the second low-pass filter has arespective adjustable corner frequency, wherein the respectiveadjustable corner frequency and a carrier frequency of the passbandsub-channel together define the guardband between the basebandsub-channel and the passband sub-channel.
 16. The method of claim 11,further comprising bandpass filtering the second subset of the datastream with a bandpass filter having an adjustable bandwidth in thepassband circuit.
 17. The method of claim 11, further comprising: at afirst converter in the baseband circuit, receiving the first subset ofthe data stream and converting the first subset of the data stream intoa first analog signal, wherein the first analog signal corresponds tothe baseband sub-channel; and at a second converter in the passbandcircuit, receiving the second subset of the data stream and convertingthe second subset of the data stream into a second analog signal. 18.The method of claim 17, further comprising multiplying the second analogsignal by a vector to produce a signal corresponding to the passbandsub-channel, wherein the vector corresponds to a carrier frequency ofthe passband sub-channel.
 19. The method of claim 18, wherein the vectorhas an in-phase component and an out-of-phase component.
 20. The methodof claim 11, further comprising combining signals in the basebandsub-channel and the passband sub-channel prior to transmission.